Conventional fiber lasers use actively doped fiber amplifiers that offer limited peak powers. Such fiber amplifiers typically include a seed laser, an active fiber or active fiber taper, one or many laser diode pumps, and a pump multiplexer. For pulsed applications, so-called large mode area (LMA) fibers are preferred to enable high peak powers by reducing nonlinear effects that are dependent on beam mode field diameter (MFD) and effective length of the amplifier fiber. Counter-pumped configurations can be used instead of co-pumped configurations to increase the threshold of nonlinearities, typically by a factor of about 3. FIG. 1 illustrates the relationship between output power, fiber length, and non-linear thresholds. For counter pumping a fiber amplifier, free space optics are typically used, requiring relatively complex fiber holding fixtures and complex free space optics. Thermal management becomes a challenge as pump power increases. For example, thermally induced mechanical drifts cause coupling losses and power-dependent (“dynamic”) beam pointing. In addition, free space optical pumping schemes require complex tooling for adjustment and alignment. Providing a suitable end cap can also be difficult as the length of the end cap is limited by the numerical aperture of the pump light and complex, bulky end caps are typically required to permit sufficient signal beam expansion to avoid optical damage.